Open Access Research Article Issue
Texture and anisotropy of hot-pressed h-BN matrix composite ceramics with in situ formed YAG
Journal of Advanced Ceramics 2022, 11 (4): 532-544
Published: 17 March 2022

Textured hexagonal boron nitride (h-BN) matrix composite ceramics were prepared by hot- pressing using different contents of 3Y2O3-5Al2O3 (molar ratio of 3:5) as the sintering additive. During hot-pressing, the liquid Y3Al5O12 (YAG) phase showing good wettability to h-BN grains was in situ formed through the reaction between Y2O3 and Al2O3, and a coherent relationship between h-BN and YAG was observed with [010]h-BN// [1¯11]YAG and (002)h-BN//(321)YAG. In the YAG liquid phase environment formed during hot-pressing, plate-like h-BN grains were rotated under the uniaxial sintering pressure and preferentially oriented with their basal surfaces perpendicular to the sintering pressure direction, forming textured microstructures with the c-axis of h-BN grains oriented parallel to the sintering pressure direction, which give these composite ceramics anisotropy in their mechanical and thermal properties. The highest texture degree was found in the specimen with 30 wt% YAG, which also possesses the highest anisotropy degree in thermal conductivity. The aggregation of YAG phase was observed in the specimen with 40 wt% YAG, which resulted in the buckling of h-BN plates and significantly reduced the texture degree.

Open Access Review Issue
Preparation and anisotropic properties of textured structural ceramics: A review
Journal of Advanced Ceramics 2019, 8 (3): 289-332
Published: 02 August 2019

Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth (TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented.

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